1. Field of Invention
The present invention relates to a light source using an organic electroluminescent (hereinafter, referred to as xe2x80x9cELxe2x80x9d) element.
2. Description of Related Art
An organic thin film EL element, that is provided with a laminate body in which at least one organic light emitting layer is interposed between an anode and a cathode, can considerably reduce the applied voltage, as compared with an inorganic EL element. Development for the purpose of obtaining an organic EL element having enhanced performance has been actively advanced through developments and improvements. Elements of various colors of light and elements high in brightness and efficiency have already been developed for organic thin film EL elements, and their use for pixels of display devices and light sources have been implemented.
The technology to reduce the profile of an illumination device that illuminates a liquid crystal display element is disclosed in Japanese Unexamined Patent Application Publication 10-50124. The technology to use an organic EL element, having a linear pattern, for a light source to illuminate the liquid crystal display device from its front side, or for a light source of a back light to illuminate the liquid crystal display device from its reverse side, is disclosed in this Japanese Unexamined Patent Application Publication.
However, problems exist in the above-described prior art technology. For example, the current supplied to the organic EL element must be increased in order to improve the brightness of the illumination light, which reduces the service life of the organic EL element since the temperature of the element rises as the current is increased.
Accordingly, an object of the present invention is to provide an illumination device that reduces the current supplied to the organic EL element in order to solve these problems.
The following organic EL light sources are provided in accordance with the invention.
An organic EL light source in accordance with an aspect of the invention includes a first organic EL element having at least one light emitting layer that is formed on a first surface of a transparent substrate that is subject to light transmissivity and light conductivity, and a second organic EL element having at least one light emitting layer that is formed on a second surface opposite to the above first surface.
In the above-described structure, the light source is formed of the organic EL element using a thin film material, and the light source can be reduced in profile and in size. In addition, a display device on which the light source is mounted can be reduced in profile and in size.
The second organic EL element can be formed at a position opposite to the above-described first organic EL element. Specifically, a light outgoing surface of the first organic EL element and a light outgoing surface of the second organic EL element can be opposite to each other.
In the above-described structure, at least two organic EL elements are formed on one substrate, and the current supplied to one element to realize a light source of the same brightness as that of a light source having one element can be reduced. Thus, advantages achieved include increasing the service life of the element, i.e., the light source, and saving power. When the same current as that of the light source having one element is supplied to the element, a brighter light source can be provided.
The above-described organic EL element can be sealed.
In the above-described structure, the service life of the element can be increased by sealing the element using a sealing member such as a seal substrate.
Portions, except at least one end face of the above-described transparent substrate, can be covered by a mirror.
In the above-described structure, the light leakage from a surface, except a surface from which the light of the light source emits, is prevented, and the light can be efficiently taken out by covering a mirror, in particular, a mirror or the like high in reflectance.
A light emitting layer of the above-described organic EL element can be striped shaped.
In the above-described structure, the organic EL light source can be reduced in profile and in size by forming a striped-shaped element, and when the organic EL light source is mounted on a liquid crystal display device or the like, the liquid crystal display device can be reduced in size.
At least two organic EL elements can be formed on at least one of the above-described first and second surfaces.
In the above-described structure, the light source can easily provide multi-color and white color light by forming at least two organic EL elements on one surface.
Two organic electroluminescent elements can be formed on one of the above-described first surface and the above-described second surface.
In the above-described structure, the higher brightness and the multi-color light of the light source can be realized more easily compared with the light source having one or two elements, since at least three organic EL elements are provided. Further, a white light source can be easily obtained by forming the organic EL elements so as to include three kinds of light emissions, i.e., red light emission, green light emission and blue light emission.
Two organic electroluminescent elements can be respectively formed on the above-described first surface and the above-described second surface.
In the above-described structure, the higher brightness and the multi-color light of the light source can be realized more easily compared with the light source having one, two or three elements, since four organic EL elements are provided. A white light source of higher brightness compared with the above light source, including the two organic electroluminescent elements formed on one of the first and second surfaces, can be obtained by forming the organic EL elements so as to include three kinds of light emissions, i.e., red light emission, green light emission and blue light emission.
Three organic electroluminescent elements can be respectively formed on the above-described first surface and the above-described second surface.
In the above-described structure, the much higher brightness and more multi-color lights of the light source can be realized more easily compared with the light source having one to five elements since six organic EL elements are provided. A white light source of much higher brightness compared with the above light sources, including the two organic electroluminescent elements formed on one or both of the first and second surfaces, can be obtained by forming the organic EL elements so as to include three kinds of light emissions, i.e., red light emission, green light emission and blue light emission.